linux-kernel - Re: [PATCH 1/2] fs/proc: show correct device and inode numbers in /proc/pid/maps

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Date:   Wed, 13 Dec 2023 19:05:52 +0200
From:   Amir Goldstein <amir73il@...il.com>
To:     Andrei Vagin <avagin@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Alexander Mikhalitsyn <alexander@...alicyn.com>,
        Christian Brauner <brauner@...nel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Miklos Szeredi <miklos@...redi.hu>,
        overlayfs <linux-unionfs@...r.kernel.org>
Subject: Re: [PATCH 1/2] fs/proc: show correct device and inode numbers in /proc/pid/maps

On Tue, Dec 12, 2023 at 9:08 PM Andrei Vagin <avagin@...gle.com> wrote:
>
> Hi Amir,
>
> On Mon, Dec 11, 2023 at 9:51 PM Amir Goldstein <amir73il@...il.com> wrote:
> >
> > +fsdevel, +overlayfs, +brauner, +miklos
> >
> > On Mon, Dec 11, 2023 at 9:30 PM Andrei Vagin <avagin@...gle.com> wrote:
> > >
> > > Device and inode numbers in /proc/pid/maps have to match numbers returned by
> > > statx for the same files.
> >
> > That statement may be true for regular files.
> > It is not true for block/char as far as I know.
> >
> > I think that your fix will break that by displaying the ino/dev
> > of the block/char reference inode and not their backing rdev inode.
>
> I think it doesn't break anything here. /proc/pid/maps shows dev of a
> filesystem where the device file resides.
>
> 7f336b6c3000-7f336b6c4000 rw-p 00000000 00:05 7
>   /dev/zero
> $ stat /dev/zero
> Device: 0,5 Inode: 7           Links: 1     Device type: 1,5
>
> I checked that it works with and without my patch. It doesn't matter, look at
> the following comments.
>
> >
> > >
> > > /proc/pid/maps shows device and inode numbers of vma->vm_file-s. Here is
> > > an issue. If a mapped file is on a stackable file system (e.g.,
> > > overlayfs), vma->vm_file is a backing file whose f_inode is on the
> > > underlying filesystem. To show correct numbers, we need to get a user
> > > file and shows its numbers. The same trick is used to show file paths in
> > > /proc/pid/maps.
> >
> > For the *same* trick, see my patch below.
>
> The patch looks good to me. Thanks! Will you send it?
>

I can send it, if you want.
I wouldn't mind if you send it with my Suggested-by though,
as you are already testing it and posting the selftest.

Thanks,
Amir.